The present invention relates to a regenerative pump in which a configuration of an impeller is improved, and a method of manufacturing the impeller of the regenerative pump
Generally, a regenerative pump is used as a small-sized pump which delivers a small amount of liquid of a low viscosity under a high pumping pressure, for example, a fuel pump for an automobile. Such a fuel pump includes a motor. It is driven by electricity generated by an alternator. Therefore, to satisfy present social demands such as saving of natural resources and environmental protection, reduction of fuel consumption (decrease of the alternator load) by improving the pumping efficiency has been an important technical problem in recent years.
A conventional regenerative pump is shown in FIGS. 34 and 35. An impeller 11 is received in a pump flow passage 13 in a casing 12, and rotated. A large number of vane members 14 are formed on the outer periphery of the impeller 11, and each vane groove 15 between adjacent two of the vane members 14 is divided axially into two by a partition wall 16. When the impeller 11 is rotated in a direction indicated by an arrow R, a fluid which has been drawn in the pump flow passage 13 receives kinetic energy from the vane members 14 and is delivered, under a pressure, in the pump flow passage 13 toward a discharge port. At that time, the fluid in each of the vane grooves 15 receives a rotational centrifugal force and flows in the vane groove toward the outer periphery, as shown by an arrow B1. Then, as shown by an arrow B2, the fluid collides against the inner wall of the pump flow passage 13 and its flowing direction is reversed. Further, the fluid flow indicated by the arrow B2 enters into another vane groove 15 on the downstream side (on the reverse side of the rotating direction) from the side surface of the impeller, and flows again toward the outer periphery. By repeating such flows, whirling flows are formed, and the fluid is pressurized and delivered toward the discharge port while whirling in the pump flow passage 13. The flows indicated by the arrows B1 and B2 in FIG. 34 are flows as viewed in a rotational coordinate system fixed on the impeller 11.
In the case of the above-described regenerative pump, the whirling flows in the pump flow passage are known to give a large influence to the pumping efficiency. In order to enhance the pumping efficiency, it is an important factor to generate whirling flows in the pump flow passage smoothly and to continue to generate and strengthen them.
With the conventional structure, however, the whirling flow indicated by the arrow B2 collides against the bottom end portion of the vane member 14 at an angle close to 90.degree. when it enters into the vane groove 15 from the side surface of the impeller. In consequence, the speed of the whirling flow is largely lowered by the bottom end portion of the vane member 14 so that the whirling flow can not enter smoothly into the vane groove 15.
Moreover, the whirling flow indicated by the arrow B2 moves out of the vane groove 15 in a radial direction of the impeller irrespective of the fact that the rotating direction of the impeller and the flowing direction of the fuel are the direction indicated by the arrow R. Therefore, the centrifugal force when the fuel flows out of the vane groove 15 can not be exerted effectively in the flowing direction of the fuel.
Furthermore, the distal end surfaces of the partition walls 16 extend to the outermost periphery of the impeller 11, so that an area which the whirling flows do not reach is formed between the distal end surfaces of the partition walls 16 and the wall surface of the pump flow passage, and that reverse flows are generated in this area, thereby deteriorating the pumping efficiency.
A fuel pump disclosed in, for example, Japanese Patent Examined Publication No. 63-63756 is known for using the regenerative pump shown in FIGS. 34 and 35.
Various shapes of impellers have conventionally been suggested as means for solving the problems of the above-described regenerative pump.
For example, a structure in which vane grooves are inclined in a direction reverse to the rotating direction, i.e., a structure in which whole vane grooves are inclined backwardly from the rotating direction is disclosed in Japanese Patent Unexamined Publication No. 57-99298.
A structure in which vane grooves are inclined and a structure in which vane grooves are formed in a spiral shape are disclosed in Japanese Patent Unexamined Publication No. 57-206795.
In Japanese Patent Unexamined Publication No. 61-210288, a structure in which partition walls are lower than vane members is disclosed.
Further, in Japanese Patent Unexamined Publications Nos. 57-81191, 57-97097 and 4-228899, impellers of blowers are disclosed, and a structure in which distal end portions of blades are inclined forwardly with respect to the rotating direction and a structure in which partition walls are lower than the distal end surfaces of the blades are disclosed.
However, in the structure in which the whole vane grooves are inclined backwardly from the rotating direction, as disclosed in Japanese Patent Unexamined Publication No. 57-99298 or 57-206795, a fluid flows out of the vane grooves in a direction backward from the rotating direction, and it is difficult to apply kinetic energy to the fluid to move toward a discharge port effectively.
Also, in the case of the vane grooves formed in a spiral shape which are disclosed in Japanese Patent Unexamined Publication No. 57-206795, a fluid flows out of the vane grooves in a direction backward from the rotating direction, and consequently, it is difficult to apply kinetic energy to the fluid to move toward a discharge port effectively.
In the structure disclosed in Japanese Patent Unexamined Publication No. 61-210288, vane members shaped like flat plates are still employed, and therefore, a fluid flows in and out of the vane grooves inefficiently in substantially the same manner as in the above-described conventional technique.
The configurations disclosed in Japanese Patent Unexamined Publications Nos. 57-81191, 57-97097 and 4-228899 involve a problem that a fluid does not flow into the vane grooves smoothly since only the distal end portions of the blades are inclined forwardly with respect to the rotating direction. Further, although these configurations are highly effective when they are used for a blower, a high efficiency can not be obtained in the case of an incompressible fluid such as fuel.
When partition walls are lower than vane members, the strength of the vane members is degraded. Especially, when an impeller is molded of a resin, it is feared that the vane members will be broken during grinding of the outer periphery of the impeller, thereby decreasing the yield. Moreover, when distal end surfaces of vane members are inclined backwardly from or forwardly to the rotating direction, it is feared that stress applied to the vane members during grinding of the outer periphery of the impeller will be increased and the vane members will be broken, thereby decreasing the yield.